1. Field of the Invention
This invention relates to a nozzle clogging detection device and method f or detecting clogging of a vacuum nozzle and erroneous mounting of the vacuum nozzle in an electronic component-mounting apparatus.
2. Prior Art
A vacuum nozzle for sucking or picking up by vacuum electronic components occasionally sucks in very small cut-off pieces of a carrier tape and solder paste from a circuit board when it picks up electronic components. The cut-off pieces and the solder paste sometimes adhere to and deposit on the inner surface of the nozzle hole of the vacuum nozzle to eventually clog the same. Further, a vacuum nozzle not corresponding to electronic components to be picked up is sometimes erroneously mounted on a mounting head of the electronic component-mounting apparatus. Such clogging of a vacuum nozzle and erroneous mounting of the same cause failure of suction or faulty mounting of electronic components.
Conventionally, in the nozzle clogging detection method of the above-mentioned kind, a pressure sensor is arranged across a vacuum passage communicating between a vacuum nozzle and vacuum suction means, and an actual pressure value detected by the pressure sensor is compared with a design pressure value thereof, whereby clogging of the vacuum nozzle or erroneous mounting of a vacuum nozzle different in diameter is detected. Further, a nozzle clogging detection method has been proposed e.g. by Japanese Laid-Open Patent Publication (Kokai) No. 6-209189, which takes an image of a nozzle hole by using a camera to detect clogging of the same.
In such a conventional method based on detection of pressures, when a vacuum nozzle with a small diameter is employed, the difference between the actual pressure value and the design pressure value of a clogged vacuum nozzle is very small, which often results in erroneous detection of the clogging. Further, the method of taking an image of a nozzle hole suffers from the problem that it is required to use not only a nozzle exclusively provided therefor in a manner adapted to the use of the camera such that a nozzle hole extends through the nozzle along the vertical axis thereof, but also lighting means for illuminating the inside of the nozzle to permit an image of the hole to be taken, in addition to a camera. This complicates the configuration of the nozzle clogging detector device to which the method is applied.
It is a first object of the invention to provide a nozzle clogging detection device that has a simple construction and is capable of accurately detecting clogging of a vacuum nozzle and erroneous mounting of a vacuum nozzle different in diameter.
It is a second object of the invention to provide a method that is capable or accurately detecting clogging of a vacuum nozzle and erroneous mounting of a vacuum nozzle different in diameter.
To attain the first object, according to a first aspect of the invention, there is provided a nozzle clogging detection device for an electronic component-mounting apparatus including a vacuum nozzle for picking up an electronic component by vacuum, the vacuum nozzle having a nozzle hole, vacuum means for drawing air via the nozzle hole of the vacuum nozzle, and a vacuum passage communicating between the vacuum means and the nozzle hole of the vacuum nozzle, the nozzle clogging detection device detecting clogging of the nozzle hole of the vacuum nozzle and erroneous mounting of the vacuum nozzle.
The nozzle clogging detection device according to the first aspect of the invention is characterized by comprising:
flow rate measurement means arranged across the vacuum passage for measuring an actual flow rate of air drawn in through the nozzle hole; and
nozzle clogging detection means for detecting clogging of the nozzle hole and erroneous mounting of the vacuum nozzle, by comparing the actual flow rate measured by the flow rate measurement means with a design flow rate of air to be drawn through the nozzle hole, the design flow rate of air being stored in advance.
According to this nozzle clogging detection device, attention is paid to the fact that when the suction pressure of the vacuum means is approximately constant, the flow rate of drawn air passing through a passage having a certain cross-sectional area is in direct proportion to the cross-sectional area of the passage. Hence, the flow rate of air drawn in through the nozzle hole is measured by the flow rate measurement means, and the result of the measurement is compared with the design flow rate of air to be drawn in through the nozzle hole of the vacuum nozzle, which was measured by using a new vacuum nozzle of an identical type and stored in advance. This makes it possible to detect the degree of clogging of the vacuum nozzle of which the flow rate of drawn air is actually measured. The flow rate measurement means may be integrated into the vacuum passage, and further, there is no need to use vacuum nozzles specially configured.
Preferably, the clogging detection device includes a vacuum valve arranged across the vacuum passage for switching between the vacuum passage communicating with the vacuum means and a nozzle hole-opening passage for opening the nozzle hole to an atmosphere, and the flow rate measurement means is arranged across a portion of the vacuum passage located between the vacuum valve and the vacuum means.
According to this preferred embodiment, when an electronic component is mounted on a circuit board, the vacuum valve is switched to connect to the nozzle hole-opening passage, whereupon a large amount of air flows into a vacuum nozzle-side portion of the vacuum passage. This makes it undesirable to install in this passage portion the flow rate measurement means which is required to measure a very small flow rate of air, since installation of the flow rate measurement means in such a place results in a faulty operation of the same. In contrast, in a portion of the vacuum passage between the vacuum valve and the vacuum means, only drawn air is allowed to flow in and hence prevent a large amount of air from flowing in. This ensures stable operation of the flow rate measurement means, thereby making it possible to measure the flow rate of air with high accuracy.
Preferably, the flow rate measurement means comprises a flow meter that includes a planar member arranged along a direction of flow of air drawn in, the planar member having an upstream-side portion and a down-stream side potion, and measures the flow rate of air based on a difference between a temperature of the upstream-side portion of the planar member and a temperature of the downstream-side portion of the planar member.
According to this preferred embodiment, it is possible to accurately measure a very small flow rate of drawn air. More particularly, it is possible to detect clogging of a vacuum nozzle having a small diameter with accuracy.
Preferably, the nozzle clogging detection means includes calculation means for calculating a difference between the actual flow rate measured by the flow rate measurement means and the design flow rate, and judgment means for judging that there occurs the clogging of the nozzle hole or the erroneous mounting of the vacuum nozzle when the absolute value of the difference is larger than a predetermined value.
Preferably, the nozzle clogging detection device includes notification means for carrying out notification of occurrence of the clogging of the nozzle hole or the erroneous mounting of the vacuum nozzle, when the nozzle clogging detection means detects the clogging of the nozzle hole or the erroneous mounting of the vacuum nozzle.
To attain the second object, according to a second aspect of the invention, there is provided a method of detecting clogging of a nozzle hole of a vacuum nozzle mounted in an electronic component-mounting apparatus for picking up an electronic component by vacuum, and erroneous mounting of the vacuum nozzle.
The method according to the second aspect of the invention is characterized by comprising the steps of:
measuring an actual flow rate of air drawn in through the nozzle hole of the vacuum nozzle; and
detecting clogging of the nozzle hole and erroneous mounting of the vacuum nozzle, by comparing the actual flow rate with a design flow rate of air to be drawn through the nozzle hole of the vacuum nozzle with each other.
According to this method, the flow rate of air drawn in through the nozzle hole is measured, and the result of the measurement is compared with the design flow rate of air to be drawn in through the nozzle hole of the same vacuum nozzle, which was measured by using a new vacuum nozzle of an identical type and stored in advance, whereby it is possible to accurately and easily detect the degree of clogging of the vacuum nozzle of which the flow rate of drawn air is actually measured.
The above and other objects, features, and advantages of the invention will become more apparent from the following detailed description taken in conjunction with the accompanying drawings.